Sliding Glass Shower Doors

For some unknown reason one of my doors came off track. I can get the wheels on top back in however the bottom piece (which is screwed onto the door) will not stay put. Even on the door will not close properly against the stripping.

ANY IDEAS or should I just go (and hopefully find) buy another bottom piece?

Sliding doors are made to lift off and set back on. To do that, the door has to be lifted so that the wheels on top are above the track where they ride, high enough that the bottom of the door clears its track and can drop in to it. I assume you probably know this already, but you didn't give much information to go on to figure what any other problem you might be having.

Some of the glass doors have a removeable bottom guide. To reinsert the door, you would have to remove that guide, reseat the door in the upper track, then, hook the guide in the lower guide notch, then reattach it to the door.